In Golf, you have the "Sunday Bag", or just the lightweight, easy to carry bag. We call this the "Sunday Box", or Day's Worth Box. It measures a mere 2 1/2" x 2 7/8" x 5/8", with a fly capacity of 60 flies.
Use this box to put a hatch of flies in, or to haul up the trail backpacking. Everyone needs a few of these!